Tension arch bridges comprising of end supports, cables or tendons, and roadway deck elements, as described in U.S. Pat. No. 4,704,754 issued to Bonasso, have been known and used for many years. The bridge supports transmit longitudinal and vertical forces to the ground. A cable is deployed in a predetermined catenary shape with its ends fixed proximate the ends of the bridge. Vertical forces on the bridge cause the bridge to flex downward, thereby tensioning the cable which increases the weight bearing ability of the structure. The bottom of the deck elements contain a plurality of open slots in which the cable passes and transmits its vertical force.
While providing benefits over conventional bridges, the tension arch bridge described in the '754 patent does not address all problems associated with a bridge having a cable deployed underneath it. The slots on the bottom of the deck elements are in a fixed position and cannot automatically align to accommodate dynamic loading of the bridge or construction irregularities of the deck elements or the bridge construction in general. Since the slots are fixed relative to the deck elements, each possible skew of the deck elements relative to the supports requires a different slot angle and thus a different deck element design.
The disclosed design of the '754 patent cannot be modified for use on existing bridge structures. The bridge must be initially designed to incorporate cables.
Further, the cable wears and rubs directly on the surface of the slot, substantially increasing the wear and stress on the cable, thereby decreasing its useful life. Another disadvantage of the tension arch bridge disclosed in the '754 patent is that the cable concentrates its vertical support force on a relatively small area on the bottom of the deck element, roughly the diameter of the cable, creating a high stress area on the deck element itself. If the high stress causes a failure in the deck element, the whole deck element must be replaced.